1. Field of the Invention
The present invention relates to a method of cleaning and an apparatus for removing organic matters deposited on a semiconductor substrate in a semiconductor device production process.
2. Description of the Related Art
As semiconductor devices are produced in increasingly higher degrees of integration, the devices are required to have increasingly higher reliability. In the process of forming semiconductor elements on a semiconductor substrate that is carried out in a plurality of film forming steps, in particular, cleanliness of the surface of the underlying semiconductor substrate is a critical factor that determines the reliability.
When forming a gate oxide film or a polysilicon film, it is a common practice to keep the semiconductor substrate in a carrier case made of a plastic material for several hours to several days depending on the operating condition of a film forming apparatus.
However, when kept in the carrier case, the semiconductor substrate is often contaminated by organic matters.
When a gate oxide film, for example, is formed on the surface of a semiconductor substrate that is contaminated by organic matters, it is known that the elements formed thereon are prone to problems such as deterioration in the withstanding voltage.
To remove organic matters deposited on the surface of semiconductor, such a method has been employed as irradiating the surface with vacuum ultraviolet light (wavelength: 254 nm) in an ozone atmosphere. This process has sometimes been carried out at a relatively high temperature of 200.degree. C. or higher.
However, when irradiating the surface with vacuum ultraviolet light (wavelength: 254 nm) in the ozone atmosphere, there has been a problem that a natural oxide film grows on the substrate before the gate oxide film or polysilicon film is formed thereon. There may also occur such a problem that raising the temperature accelerates the growth of the natural oxide film.
The natural oxide film is not of a good nature, and may affect the reliability of the gate oxide film or the polysilicon film to be formed later.